1. Field of the Invention
The present invention relates to a microprocessor system and more particularly to a bus interchange circuit which allows external systems to gain control of a microprocessor's busses.
2. Description of the Prior Art
Older microprocessors, such as Intel's 8-bit 8080A and 8085A provide bus interchange functions such as hold request and hold acknowledge. These functions are not available in current state-of-the-art microprocessors, such as Intel's 8086. These microprocessors however, do have a control lead for use by co-processors, such as Intel's 8089 Input-Output Processor and Intel's 8087 Numeric Data Processor. This lead can also be used as a bus interchange "handshake" control lead by emulating the pulse sequences produced by the co-processors. Thus, hold request and hold acknowledge functions, can be provided by state-of-the-art microprocessors through use of a circuit which emulates the "handshake" operation of a co-processor.
Accordingly it is the object of the present invention to provide a bus interchange "handshake" control circuit for use with a state-of-the-art microprocessor.